The present invention relates to improvements in workpiece handling apparatus for sewing machines. Sewing machines normally have a feed mechanism which advances the material continuously or stepwise past the stitching mechanism so that consecutive stitches will be evenly spaced. The most common type of feed mechanism is the reciprocating lower feed dog disposed in an opening of the work surface of the sewing machine. The feed dog unusually advances the underlayer of material stepwise. A puller or puller mechanism is often added in industrial sewing machines to advance the top surface of the material. For example, pullers (so called because they are located downstream of the stitching area) are frequently used for sewing bulky material. In this case, the puller is driven in synchronism with a feed dog engaging the undersurface of the material to achieve relatively uniform motion for the entire thickness of the workpiece as it passes through the stitching area. In some machines a synchronously reciprocating feed dog is arranged to engage the top surface of the material. Examples of top feed dog mechanisms are shown in U.S. Pat. Nos. 3,530,809 and 3,995,571 to Robert E. Porter.
In a conventional sewing machine upper and lower horizontal arms are connected at respective ends to an upright base, and the stitching area is defined between the other ends of the arms. Normally the lower arm and upright base rest on a table and support the machine. The coacting upper and lower parts of the stitching mechanism are connected to a source of drive power through the respective horizontal arms. The resulting U-shaped configuration provides positive mechanical linkage between the two parts of the stitching mechanism while affording a work area large enough for most sewing tasks. Normally when sewing one part of the workpiece, the lateral trailing portion of the material is hand-fed over the top of the lower arm as necessary. Advancing the lateral trailing position permits it to keep up with the sewn portion to avoid impeding the stitching progress. Where the stitching is extremely fast or the lateral trailing portion is extremely large or of unusual configuration, feed problems can arise. One such operation involves a long flexible tubular workpiece where the object is to provide stitching encircling the outer surface between the ends of the workpiece. First, the lower arm must be fully cantilevered from the upright base to permit the arm to receive the workpiece like a sleeve. However, even then, the length of the lateral trailing portion of the workpiece and its close fit around the lower arm combine to interfere with the feed. Thus this sewing task--circumferential tube stitching--is one for which conventional sewing machines are unsuited for mass production where frequent feed problems should be eliminated by proper machine design.
Accordingly, the primary object of the present invention is to provide an improved workpiece handling system for a sewing machine for circumferentially stitching a tubular workpiece.